asn1: Include <errno.h> before using/checking bits from it

asn1: Include <errno.h> before using/checking bits from it

Origin: upstream, https://github.com/heimdal/heimdal/commit/2194be6c9259f79b97131cec8ae44e1180b4f309
Forwarded: not-needed

Commit 232c936ea3eabfd702aaaa106ddf9474f231d776 added a fallback ENOTSUP
definition. The check itself and the fallback definition rely on
<errno.h> to be included already, so in case it was not (depending on
the platform) then there will be a wrong definition of ENOTSUP.

Instead of rely on <errno.h> to be included before including a
generated header from this tool, include it manually. This way both
the ENOTSUP check and its fallback definition (if ever) will always
work.

Gbp-Pq: Name heimdal-errno-include.patch